Omnidirectional horn radiator for beacon antenna



Dec. 31, 1963 c. CARSON 3,116,485

OMNIDIRECTIONAL HORN RADIATOR FOR BEACON ANTENNA Filed June 27, 1960 4Sheets-Sheet 1 A Trae/@Kr Dec. 31, 1963 c. cARsoN 3,116,485

OMNIDIRECTIONAL HORN RADIATOR FOR BEACON ANTENNA Filed June 27, 1960 4Sheets-Sheet 2 IN VEN TOR. Uf/Qa bezem/v Dec. 31, 1963 c. CARSON3,116,485

OMNIDIRECTIONAI.. HORN RADIATOR FOR BEACON ANTENNA Filed June 27, 1960 4Sheets-Sheet 3 Dec. 31, 1963 C. CARSON 3,116,485

OMNIDIRECTIONAL HORN RADIATGR FOR BEACON ANTENNA Filed June 27, 1960 4Sheets-Sheet 4 \7/ INVENToR.

Unite States arent tice 3,116,435 OMNDEXECTIONAL HGRN RADIATGR FR BEACONANTENNA Cyril Carson, Philadeiphia, Pa., assigner to I-T-E CircuitBreaker Company, Philadelphia, Pa., a corporation 'of Pennsylvania FiledJune 27, 196i), Ser. No. 39,669 S Claims. (Cl. 343-754) This inventionrelates generally to omnidirectional transmitting antenna for microwavesignals, and more particularly relates to novel horn radiators withtoroidal configurations that effectively radiate Tacan navigationalradio patterns.

The Tacan system derives from the military tactical air navigationsystem for aircraft. It utilizes the UHF range of 96C; mc. to 1215 mc.The Civil Aeronautics Administration now requires that Tacan transmitterantennas be directly adaptable to efficiently transmit the patternedsignals over any frequency in the low band (960 to 1024 rnc.) or highband (1150 to 1215). A suitable radiator therefore needs to berelatively broadbanded. A further important requirement is that thetransmitted Tacan pattern be effective over an elevation range from thehorizon to at least 60 above the horizon.

Prior antennas that provide the correct azimuth pattern generally failto give a suitable vertical radiation pattern. A further seriouslimitation has been that the phase of the signal components thatconstitute the Tacan azimuth pattern was not constant with frequencyover the bands. Critical dimensional relations with frequency preventedtheir general application over the Tacan bands as a particular antennasuitable for transmitting at a specific frequency, would radicallydistort the requisite pattern if used at a different frequency, evenwith moderate alteration.

The antenna of the present invention overcomes the aforesaid prior artshortcomings. The modulation of the carrier wave required for theazimuth is effected within a relatively small radius, and the energy isthereupon radiated over a suitably shaped toroidal aperture oromnidirectional horn. The 360 horn configuration of the invention isstationary, and is coupled to the central modulation unit through a pairof parallel discs. The horn aperture is circular in the XY plane, andcan be suitably ared in the Z or vertical plane to obtain a desiredVertical radiation characteristic.

The radius of the omnidirectional. radiator hereof controls the match ofthe signal components to free space. By utilizing a relatively largeradius, at least about seven times wave length the lowest carrierfrequency used, excellent radiation characteristics result over thewhole Tacan operation range. The modulator of relatively small radius ismade concentric within the horn. The vertical height of the hornaperture is preferably made about half-wavelength or greater. There isno feed-back to the coupling system, and the radiation is practicallyall outwardly in the desired pattern.

The invention radiator is not critical or frequency selective over arelatively broadband for UHF signals. It is eicient, stable, andmechanically rugged. The principles and features of the inventionsystem, to be set forth in more detail, permit one to construct aradiator with any one of a wide diversity of omnidirectional radiationpatterns. It is relatively simple to meet the rigid requirements of theCAA stated herein above, therewith, where a rotating central modulatoris used a toroidal choke couples the stationary discs for the horn withthe peripheral region of the modulator.

It is accordingly a principal object of the present invention to providenovel toroidal radiators of microwave signals.

Another object of this present invention is to provide novelomnidirectional horn radiators suitable for producing Tacan systemradiation patterns.

A further object of this present invention is to provide novel 360 hornradiators eliicient over a relatively broadband of UHF signals.

Still another object of this present invention is to provide novelomnidirectional horn radiators that are efficient, and with a verticalradiation characteristic effective up to at least 60 to the horizon.

Still a further object of this present invention 1s to provide novelomnidirectional horn microwave radiation systems that are relatively ofsimple construction, and rugged.

These and other objects of the invention will become more apparent fromthe following description of exemplary embodiments thereof, illustratedin the drawings, in which:

FIGURE 1 is a polar representation of an idealized Tacan radiationpattern, in a single elevation plane.

FlGURE 2 is a polar representation in an azimuth plane of the Tacanmodulated signal pattern.

FIGURE 3 is a diagrammatic illustration in perspective of an XYomnidirectional signal source.

FIGURE 4 is a plan view of an XY signal source like that of FIGURE 3,with a modulator to produce a Tacan signal pattern.

FIGURE 5 is an enlarged cross-sectional View through the line S--5 ofFIGURE 4, illustrating a modular element.

FIGURE 6 is a partial plan view of an exemplary form of the hornradiator system of the invention.

FIGURE 7 is an enlarged cross-sectional view taken along the line 7-7 ofFIGURE 6.

FIGURES 8 through 19 are illustrations of a number of exemplaryconfigurations that the invention horn radiator may embody, andaccompanying polar representations of the corresponding radiationpatterns.

The CAA specifications for the radiated Tacan pattern is represented inpolar form in FIGURE 1, in an elevation plane. Rad-ial distance from theorigin represents signal field strength as a function of elevationangle. The minimum requirement pattern is outlined as follows: startingat the origin O, by the horizontal abscissa 21 to point 25:corresponding to six db gain over an isotropic course by an arc 26 topoint 27, 5"v above the horizon by cosecant line 2S parallel to thehorizon to point 29, 60 above the horizon, and by a radial line 30 tothe origin O. Radiation pattern 2) is a typical One, that encloses theminimum requirement pattern, and thus meets the specifications.

The basic Tacan signal pattern 35 comprises a uniform nine lobed spatialmodulation 31, 31a as shown in FIGURE 2. The zero cycle is representedby the broken circle 32 centered at C. A one cycle modulation is seen asessentially circular at 33, with its center at C displaced from thereference center C. Polar curve 35 is for a typical azimuth plane withpoint C as origin. 'Ihe radiation per pattern 35 is rotated about originC to effect the Tacan system operational signal distribution, inazimuth. The vertical distribution is represented by the polarconfiguration 20 of FIG- URE 1.

The Tacantype spatially modulated signals are generated by a suitablerotatable modulator. Reference is made to the copending patentapplications Serial Number 742,646, filed June 17, 1958, entitledBroad-Band Antenna, inventor David F. Bowman, now Patent No. 2,990,545;and Serial Number A809,690, filed April 29, 1959, entitled Micro-WaveStrip Line Modulator, in-

ventor David F. Bowman, both assigned to the assignee of the instantapplication for illustrations thereof. The omnidirectional radiators Vofthis invention may be used with such, and other omnidirectionalmodulators or generators. The spatial carrier modulator' 50 incorporatedin the exemplary radiator system illustrated in FIG- URES 6 and 7,corresponds to that described more fully in Vthe aforesaid copendingpatent application, S. N. 742,646.

Reference is now made to FIGURES 3, 4 and 5 for an understanding of theoperation of such modulators. FIGURE 3 `illustrates converter 40 that isfed with a UI-IF or microwave signal S at central coaxial transmissionline 41. Two spaced metal discs 4Z, 43 are individually connected to the-two terminals of coaxial line 41. A uniform axial Yor 360 signalpattern is projected by the transmission discs 42, 43, as indicated bythe radial lines 45. Rotation of the disc array 42, 43 as indicated byarrow a effects a direct spatial rotation of the source pattern `4S.

The signals from source S0 impinge at center c of the discs 41, 42, andthen radiate across the discs to their perimeters, as will be understoodby those skilled in the art. To effect the multi-lobed spatialmodulation for the Tacan modulator Si), a series of beam modulatorelements 51 are incorporated across a set of spaced discs 52, 53 asshown in FIGURES 4 and 5. Elements 51 are arranged in the peripheralregion to modulate an incident uniform radial carrier signal with thenine multiple lobes (31, 31a) in accordance with FIGURE 2. The modulatorelements 51 may be bolts secured through opposed apertures in the discs.

Nine uniformly positioned modulator elements 51 produce the requisitelobes. A tenth modulator element 54 is located radially closer to centerc, and constitutes the fundamental modulator corresponding to curve 33of FIGURE 2. A layer 55 of low dielectric loss material is sandwichedbetween discs 52, 53 for mechanical advantage. Suitable materialtherefore is polyfoam, Styrofoam, etc. As hereinabove stated, theparticular omnidirectional signal pattern, or the spatial modulatorsource, utilized for the unit 50 in conjunction with the omnidirectionalradiator system of this invention, is optional.

The exemplary omnidirectional radiator system is illustrated in FIGURES6 and 7. The rotatable modulator 50 is centrally positioned within theannular horn radiator 60. As will be described in detail, the shape andflare of toroidal horn 60 may assume many forms for desired radiationpatterns. Horn 60 comprises two -annular sides 61, 62 extending fromrespective parallel metal discs 63, 64 which are mounted as a stationaryassembly. Efficient electrical coupling is effected between the discradial transmission line 63, 64 and the peripheral signal output ofrotatable modulator 50 through annular chokes 65, 66. Chokes `65, `66are proportioned to produce an electrical short circuit acrossrespective plates 53, 63, and 52, 64 despite the mechanical breakthereacross. Electrical signal continuity is thus maintained betweenmodulator 50 when rotated, and the stationary discs 63, 64. No signalleakage takes place in view of the peripheral location of the chokes 65,`66.

The carrier signal (fo) is fed to the modulator discs 52, 53 through acoaxial transmission line composed of rotatable shaft 70 and a metaltube 71 concentric therewith. The top end 70 of shaft 70 is secured withthe center of disc 53 at 68, and forms a terminal for microwave input.Sleeve 71 has -its rim connected along a corresponding central apertureat 71 with lower disc 52, to complete the RF coupling. The shaft 7? isconnected by coupling 72 to drive motor 73. Rotation of motor 73, as inthe direction of arrow a, rotates modulator 50 as a unit, includingshaft 70, discs 52, 53 with dielectric layer 55, modulator elements 51a,and sleeve 71. A bearing 74 supports sleeve 71 in the vertical rotation.

The basic carrier signal (fo) is fed to modulator through the rotatablecoaxial line 70, 71 connected therewith, through a rotary joint coupler75. The carrier signal is coupled to coupler '75 across end flange 7 6.For Tacan transmission modular -56 is rotated at 900 r.p.m. Nine modularelements indicated at 51a, produce the nine lobes per FIGURE 2. Theazimuth pattern of the signal s output of the rotating modular 50 may beeX- pressed as:

:A14-A2 COS COS where: A1, A2 and A3 are suitably chosen constants and 0is the angle measured about the modulator periphery.

The modulated signals a radially pass through outer discs 63, 64 to horn60, and are controllably radiated as indicated at s' in FIGURE 7.

FIGURE 8 illustratesv a vertical section of a typical horn configurationcontemplated by the present invention, corresponding to the annular horn601 of FIGURES 6 and 7. Omnidirectional radiator '80 comprises two metaldiscs 81, 82 spaced apart by distance S. The horn sides 83, 84 extendfrom plates l81, S2 by equal angles 0, in ared relation. The verticalheight A of the horn aperture is an important dimension in the inventionsystem. For an effective vertical pattern. whereby appreciable signalstrength is radiated up to at least above the horizon, the dimension Ais made at least equal to }\-:2, where A is the wave length of thecarrier frequency for which the system is to be used.

In Tacan transmitters, such lowest frequency is 960 mc., where the wavelength A is about one foot. Thus for Tacan fullband operation, A is madeat least 6 inches, and

preferably greater. Also, importantly, the angle 0 of the horn sides 83,84 is preferably less than about 25, to create the vertical patternrequirements for Tacon. The angle 0 is not critical in `this regard, aslong as less than the 25 figure. However in particular cases, `a greaterthan 25 angle is useable.

The preferable minimum for dimension A may be reduced from the )\+2figure where efficiency is not important. The length L of the horn sidesi83, 84 are equal, and established once the other parameters 0, A and Sare selected. The amount of spacing S is not critical, and is optionalin the invention system. The polar curve 85 is a representation of thesignal s pattern radiated by horn where 0 is 25 or less, and A is A+?.or greater.

A further important dimension of the invention array is the radius R ofthe horn 83, 84 from the center 618 of the system, see FIGURE 6. Theradius R controls the match of the multi-lobe frequency component A3 cos90 to free space, and the cross-polarized components thereof. It isdesirable to keep R large in relation to the wavelength k of the carrierfrequency, namely cos 0. A preferable relation is to make the Rdimension at least 7 times the wavelength of the lowest carrierfrequency used. For a Tacon broadband array, R is preferred to be atleast seven feet, making the horn 60 diameter about l5 feet in theexemplary radiator. Smaller diameters are of course usable, but are lesseicient in giving coverage to high elevation angles for the l9 cyclecomponent.

It is thus now apparent to those skilled in the art that the inventionarrangement, while having preferred dimensional relationships, isneither selective or critical frequencywise. A reasonably broad-bandradiator is practicable, with no problem over the Tacan `range of 960 to1215 mc. One omnidirectional arrangement hereof will efficiently andeffectively handle all Tacan transmitter frequencies, and their higherfrequency components. To alter the operation frequency of the radiatorsystem, it may be necessary to modify the modulator array 50; theinvention section coupled thereto need not be changed. The bolt type 51modulator elements would need simple repositioning. 'Ihe inventionradiator system is of course useable for other than Tacanomnidirectional applications.

With horn aperture the dimension A at least )\+2, there is negligiblefeed-back on leakback of signal to the radial transmission discs, andradiation is practically all outwardly. This resul-ts in high radiationefliciency. With the radius R dimension at least 7k, there is nodeterioration of the higher frequency signal components (A3 cos 90).There is thus no phase distortion among the Tacan signal componentsradiated thereby. Also, making the horn side flare angles not `greaterthan about 25% insures suitable signal strength to the 60 elevationreferred to.

The horn radiator 90 of FIGURE 10 has equal horn sides 91, 92 eachextending by the same vangle 0, from horizontal discs 93, 94 to anaperture A1. The value of 0 is shown at 35, being substantially langerthan that of 0 of FIGURE 8 at 25. The result is to atten the patternradiated, as shown by polar curve 95 in FIGURE 1l. Further enlargrnentsof the flare angles 0, of sides 91, 92 would still further atten thisoutput pattern. In special applications where such is desired, thisprinciple may be utilized.

With the are angles reduced to a lower value than that of 0 of FIGURE 8,a further bulge occurs in the radiated pattern, as indicated by polarcurve 105 of FIG- URE 13. The corresponding smaller angle 02,illustrated in FIGURE l2 -at 10 gives such result. The unit 100comprises a shallow ared horn 101, 102 extending symmetrically fromdiscs 103, 104. =It is to be noted ythat the radiation patterns 85, 95and 105 are `all symmetrical about the horizontal. This in turn is dueto the symmetrical arrangement of their corresponding horn radiators.

The radiation patterns may be readily tilted to the horizontai with theinvention system. One method is to use a diiferent are angle for thehorn sides. This is illustrated by horn 110 in FIGURE 14. The angle 03of horn side 111 to disc 113 is greater than angle 04 of side 112 todisc 114. The sides 1111, 112 extend equally to radius R, and formaperture A3. The lengthe L3 and L4 of these sides are determined oncespacing S is selected. The resultant pattern 115 is tilted upwardly byan angle 1 as noted in FIGURE 15. This tilt angle is controlled by theselected angles 03 and 04.

Another way to tilt the radiated pattern is shown by horn system 120 ofFIGURE 16. 'Ihe lower horn side 121 is made longer (LB) than that of(LA), the upper one 122. Also, lower side 121 is an extension of disc123, and upper horn side 122 is at an angle 05 to disc 124. The resultis pattern 125 of FIGURE 17 with a tilt angle 2 greater than an angle 1of FIGURE 15. The degree tilt p2 is controlled by .the relativeproportioning of La to Lb and In FIGURE 18, the lower horn side 131 ofarray 130 is longer than side 132, as in horn 120, but is ared by anangle 07 to disc 133. Upper side 132 is arranged at an angle 03 to disc134, greater than 07. A tilted pattern in the manner of FIGURE 17results. The relative lengths of the horn sides are more effective inproducing the tilt than the relative angles thereof. A further form ofhorn array for radiation pattern tilting is shown at 140 in FIGURE 19. Asymmetrical horn arrangement 141, 142 extends from discs 143, 144. Atoroidal lens 145 is positioned between horn sides 141, 142 suitablyshaped to slow down the waves along the upper horn section, as alongside 141. The lens 145 is seen to be thicker at its base 146 contiguouswith side 141. Lens 145 is of lowloss dielectric material, aspolystyrene, Teflon, etc.

In summary, it is now evident that a wide variety of radiation patterncharacteristics can be obtained by suitable shaping of the horn aperturein the vertical or Z plane. Further, the opposed horn sides may be madecurved in conventional horn practice. The aperture of the horn antennahereof can be considered equivalent to ring layers of local electric andmagnetic currents, the amplitude of which is a function of azimuth angleand is directly related to the azimuth pattern. With the aperturevertical height (A) at least )\+2, there is little feed back effect, andthe radiation pattern can be considered to be due entirely to suchelectric and magnetic current rings associated With the aperture. Withthe radius (R) of the horn aperture suiiiciently large, all componentsin the azimuth pattern produce essentially the same vertical pattern.

While this invention has been described in connection with exemplaryembodiments, it is to be understood that it may be practiced withmodifications and variations that fall within the broader spirit andscope of the invention as defined in the following claims.

I claim:

l. An omnidirectional horn radiator system for microwave signalscomprising a pair of stationary planar discs spaced for forming a radialsignal transmission line effective over 360 in the azimuth plane, theremote radial regions of said discs being shaped with an annularoutwardly ared aperture constituting a horn radiator of signalsimpressed across said discs having a predetermined vertical radiationpattern throughout the omnidirectional azimuth sweep of the radiator,said discs each being formed with a central aperture, and a rotatablesignal modulator source of annular shape concentric to said discs andelectrically coupled to said discs across their aperture periphery foromnidirectional radiation to free space of the signals in saidpredetermined pattern, the diameter of said discs being sucientlygreater than the wavelength of Said signals for providing means forbroad-band omnidirectional matching to free space, while permittingsubstantial aperture variation for transverse beam shaping.

2. An omnidirectional horn radiator system, as claimed in claim l, inwhich the radius of said aperture to the radiator center is at least theorder of seven times the wavelength the lowest frequency of saidsignals; said signal modulator being of a substantially lesser diameter.

3. An omnidirectional horn radiator, as claimed in claim l, in which theangle of one of the aperture walls is less than the order of 25 withrespect to the plane of its associated member.

4. An omnidirectional horn radiator, as claimed in claim '1, in whichthe angle of the aperture walls are each less than the order of 25 withrespect to the plane of its associated disc.

5. An omnidirectional horn radiator, as claimed in claim 1, in which theupper aperture annular wall is at a greater angle to the discs than isthe lower aperture wall and the lower annular aperture wall issubstantially longer radially than the upper one for producing avertical radiation pattern with its longer axis tilted above thehorizon.

6. An omnidirectional horn radiator, as claimed in claim 1, in which theradius of said aperture to the radiator center is at least the order ofseven times the wavelength the lowest frequency of said signals; thelower annular aperture Wall is substantially longer radially than theupper one, and wherein the aperture height of the effective annular hornis at least of the order of one-half that of said wavelength.

7. An omnidirectional radiator, as claimed in claim 1, further includinga lens of dielectric material arranged in said aperture for producing avertical radiation pattern With its longer axis tilted above thehorizon.

8. An omnidirectional horn radiator, as claimed in claim l, furtherincluding a lens of dielectric material and toroidal form arranged insaid aperture with a thicker section adjacent the upper aperture wallfor producing a vertical radiation pattern with its longer axis tiltedabove the horizon.

(References on following page) References Cited in the le of this patentUNITED STATES PATENTS King May 26, 1942 Tinus Apr. 17, 1951 5 LitchfordAug. 21, 1951 Litchford Aug. 2S, 1951 Litchford Sept. 11, 1951 FOREIGNPATENTS Great Britain Dec. 31, 1952

1. AN OMNIDIRECTIONAL HORN RADIATOR SYSTEM FOR MICROWAVE SIGNALSCOMPRISING A PAIR OF STATIONARY PLANAR DISCS SPACED FOR FORMING A RADIALSIGNAL TRANSMISSION LINE EFFECTIVE OVER 360* IN THE AZIMUTH PLANE, THEREMOTE RADIAL REGIONS OF SAID DISCS BEING SHAPED WITH AN ANNULAROUTWARDLY FLARED APERTURE CONSTITUTING A HORN RADIATOR OF SIGNALSIMPRESSED ACROSS SAID DISCS HAVING A PREDETERMINED VERTICAL RADIATIONPATTERN THROUGHOUT THE OMNIDIRECTIONAL AZIMUTH SWEEP OF THE RADIATOR,SAID DISCS EACH BEING FORMED WITH A CENTRAL APERTURE, AND A ROTATABLESIGNAL MODULATOR SOURCE OF ANNULAR SHAPE CONCENTRIC TO SAID DISCS ANDELECTRICALLY COUPLED TO SAID DISCS ACROSS THEIR APERTURE PERIPHERY FOROMNIDIRECTIONAL RADIATION TO FREE SPACE OF THE SIGNALS IN SAIDPREDETERMINED PATTERN, THE DIAMETER OF SAID DISCS BEING SUFFICIENTLYGREATER THAN THE WAVELENGTH OF SAID SIGNALS FOR PROVIDING MEANS FORBROAD-BAND OMNIDIRECTIONAL MATCHING TO FREE SPACE, WHILE PERMITTINGSUBSTANTIAL APERTURE VARIATION FOR TRANSVERSE BEAM SHAPING.